The present invention relates to constrained vane rotary compressors. Machines of this type are typically comprised of a rotor mounted within a cylindrical stator, the mounting being such that the rotor axis is offset from the cylindrical axis of the stator. The rotor contains a plurality of slideable vanes such that the vanes may move radially with respect to the rotor axis. As the vanes rotate within the stator, they are guided such that their distal ends come close to, but do not physically engage the interior surface of the cylindrical wall of the stator. Typically, cam tracks are formed or placed in the end walls of the stator which guide the rotating vanes by means of rollers or cam followers residing in the cam tracks. The two opposing cam tracks, each situated in a stator end wall, restrain the vanes from physically contacting the interior stator wall. Such an arrangement in conjunction with an offset rotor allows the machine to operate as either a compressor or expander as the particular application necessitates. When the machine operates as a compressor, regions of varying pressure are formed between the periphery of the rotor and the stator interior wall. Regions of lowest pressure exist near the compressor's inlet port, and highest pressure regions formed near an outlet port.
There are several disadvantages in providing cam tracks in end walls of the stator. The first is that by forming tracks in the end walls, the seal between the lateral edges of the vanes and the end walls of the stator is interrupted, making it possible for gas to pass from a high pressure region on one side of a vane to a lower pressure region on the other side of the vane, by leaking past the vane through the cam tracks. In addition, the cam tracks erode the sealing area between the rotor and the end walls and allow leakage. Such leakage decreases compressor efficiency.
Another disadvantage stems from the large number of bearing or contacting surfaces between cam tracks and numerous cam followers. The cam follower may comprise a rolling element mounted on a respective vane via a stub axle. The rolling element contacts a cam surface residing in a cam track. Each vane typically contains two cam followers, each situated on an opposing side of a vane, and each residing within one of the cam tracks in the end walls of the stator. The surface that the rolling element may contact, a race, may either be stationary or rotatable with respect to the stator housing. In either situation a large number of bearing or contacting surfaces results. This is evident by noting that with each vane there are at least two bearing assemblies, one on each stub axle affixed to a rolling element. Additionally, if the cam track has a rotating race the quantity of bearing surfaces further increases. The large quantity of bearing assemblies required in machines of the present type result in added complexity in the manufacture of such machines and greater opportunity for mechanical failure.